This invention relates to the joining of metals, and, more particularly, to the use of an amorphous intermediate bonding element to effect the joint.
Most of the applications of metals in structures require their joining to other metals in some fashion, and a large number of approaches are in use. Some joining techniques use fasteners such as bolts, rivets, screws, and the like. Other joining techniques use direct metal-to-metal bonds, bonds with an intermediate adhesive layer, or bonds with an intermediate metallic joining layer. The latter category includes the known techniques of welding, brazing, and soldering. The present invention relates to an improved joining technique using an intermediate metallic joining element placed between the pieces being joined.
Existing joining techniques of this general type have significant shortcomings when used in particular applications. In welding, the pieces being joined are typically locally melted in the region of the joint and fused with a filler metal. Depending upon the metals being welded, the filler metal, the weld processing, and the skill of the welder, the final welded joint can exhibit undercutting, porosity, incomplete fusion, incomplete joint penetration, excessive melt through, weld cracking, and cracking in the heat affected zone. The composition and microstructure of the pieces being joined are locally altered from their desired conditions, and are typically weaker and more susceptible to corrosion than before joining. Consequently, the welded joint is often the site of the initiation of failure in service.
In soldering and brazing, a layer of a metal that is more noble and has a lower melting point than the pieces being joined is flowed between the pieces. Soldering and brazing are similar operations in the sense that they rely upon the adhesion of the solder or braze layer to the pieces to effect the joint. Fluxing of the surfaces of the pieces being joined aids in attaining reasonable strength in the joint. The solder and braze alloys are normally relatively weak compared to the structural alloys of the pieces being joined, and are quite often more brittle than the structural alloys. A sufficiently high strength for most structural applications is achieved only when the joint is very thin, on the order of a few thousandths of an inch, resulting in a triaxial stress state in the joint. Soldered and brazed joints can suffer many of the problems of welded joints, such as porosity, incomplete bonding, microstructural changes, and dependence upon operator skill. As with welded joints, structural failure often occurs at the soldered or brazed joints.
There is a need for an improved approach to the joining of metals using an intermediate joining layer. The technique would desirably avoid the problems discussed for other techniques of this type. The present invention fulfills this need, and further provides related advantages.